1990 in Roman numerals

How MCMXC is built

Roman numerals are written one decimal place at a time, largest first.

1. Mthousands · 1M is 1,000.
2. CMhundreds · 9C before M means 1,000 − 100 = 900. This saves writing DCCCC.
3. XCtens · 9X before C means 100 − 10 = 90. This saves writing LXXXX.

1,000 + 900 + 90 = 1,990

The pairs CM and XC use subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction

Mistakes to avoid

• Not MXM. It looks like a shortcut, but X may only come before L or C, not M. The correct form is MCMXC.
• Not MDCCCCLXXXX (11 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today MCMXC (5 letters) is the standard.
• There's no letter for zero. The zero is simply left out, which is why 1990 has 3 parts, not 4.